Since the introduction of chromosomal banding techniques in the early 1970's, numerous tumors have been associated with specific chromosomal defects. Prezygotic chromosomal deletions have been causally related to two specific childhood tumors (retinoblastoma and Wilm's), while a large number of hematopoietic neoplasms have been associated with site-specific translocations or complete or partial monosomy. Less is known about the chromosome abnormalities of solid tumors because it has been technically difficult to obtain chromosome preparations from them. As a result of recent improvements in cytogenetic techniques, there is now also evidence for specific changes in solid tumors. The major role of the Cytogenetics Core will be to prepare karyotypes from the tumors provided by the Tumor Procurement Core, and to coordinate the established and distribution of explant cultures of these tumors with matched normal control tissues for the appropriate investigators. The data on the tumor karyotypes will also be provided to the Tumor Procurement/Data Management Core. These studies should add to the growing body of knowledge regarding nonrandom cytogenetic changes in pediatric solid tumors and their utility in diagnosis.